This invention relates generally to components for electronic circuits and. more particularly to multi-layer surface-mount capacitors.
Two types of surface-mount capacitors are typically used in the design of electronic circuits. They are multi-layer capacitors (MLCs) and single layer capacitors (SLCs). MLCs typically have a capacitance value in a range of 0.1 pico-Farads to 0.2 micro-Farads or more while SLCs typically have a capacitance value of less than 0.05 pico-Farads to 1800 pico-Farads or more.
The choice of the type of capacitor depends on the electrical characteristics required. An MLC has a low insertion loss at low frequencies and therefore has a good low frequency response. In contrast, an SLC has a low insertion loss at high frequencies and therefore has a good high frequency response. In some cases it is desirable to combine the characteristics of both the SLC and the MLC to obtain a broadband device. This is typically done by putting an MLC component and an SLC component electrically in parallel with each other. However, simply mounting an MLC component and a separate SLC component adjacent each other on a substrate, splitting the electrical trace entering the capacitors and recombining the electrical trace on the opposite side of the capacitors results in losses which are unacceptable at high frequencies.
Another method which has been utilized for putting an MLC electrically in parallel with an SLC is to mount an MLC on top of an SLC. However, there are problems inherent in this method because MLCs and SLCs are of significantly different physical size. To overcome the size difference, an SLC is mounted with one end in contact with a first side of an electrical trace and the second end is connected to the second side of the electrical trace by a flexible connection. An MLC is then mounted at an angle over the-SLC such that it is mounted directly in contact with the second side of the electrical trace and is connected to the first side of the electrical trace by a flexible connection. Although this configuration has enhanced electrical characteristics, it is expensive to manufacture. Rather than being assembled by an automated pick-and-place machine, this configuration must be assembled manually.
The present invention is directed to an improved hybrid capacitor. The capacitor combines the functionality of an SLC and an MLC into one electrical component. An MLC is typically composed of interleaved electrically conductive plates which are alternatively electrically connected to one of two electrical terminations. at opposite ends of the capacitor component. The interleaved plates are spaced apart by a dielectric material which may also cover the outer surfaces of the outer-most plates. Where the plates are not equidistantly spaced, several different dielectric materials may be used between the pairs of plates of the MLC.
An SLC is created in the same componeat by substituting a different dielectric material to cover one of the outermost plates and extending an additional interleaved plate on the outside of the different dielectric material. In addition to the change in the dielectric materials the additional plate on the outside of the different dielectric material may have a significantly different geometry than the interleaved plates. In particular, it may only overlay the next adjacent plate slightly. Additionally, the next adjacent plate may be altered in geometry to further alter the electrical characteristics of the SLC, such as mug the next adjacent plate wedge shaped. The result is that the SLC has a significantly different capacitance value than the MLC.
Advantageously, the functionality of two electrical components, an SLC and an MLC, have been combined into one electrical component which can be used in high speed applications as a direct current blocking-capacitor or for broadband decoupling on power supply rails.
Also advantageously, the component of the present invention can be mounted on a substrate by the use of an automated pick-and-place machine. The time and cost required to mount the individual component is less than required to mount separate components.
A further advantage-of the present invention is that it has improved electrical performance over prior options. Specifically, the choice of dielectric material and plate configurations can be chosen to produce an insertion loss that is minimized and has a flattened response to frequency. The dielectric material used between the plates of the SLC can be chosen to achieve the desired high frequency response while the dielectric material used between the plates of the MLC can be higher such that the low frequency insertion loss would be small.
Other aspects and features of the invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.